Many-body Green's function theory for thin ferromagnetic films: exact treatment of the single-ion anisotropy

Abstract

A theory for the magnetization of ferromagnetic films is formulated within the framework of many-body Green's funtion theory which considers all components of the magnetization. The model Hamiltonian includes a Heisenberg term, an external field, a second- and fourth-order uniaxial single-ion anisotropy, and the magnetic dipole-dipole coupling. The single-ion anisotropy terms can be treated exactly by introducing higher-order Green's functions and subsequently taking advantage of relations between products of spin operators which leads to an automatic closure of the hierarchy of the equations of motion for the Green's functions with respect to the anisotropy terms. This is an improvement on the method of our previous work, which treated the corresponding terms only approximately by decoupling them at the level of the lowest-order Green's functions. RPA-like approximations are used to decouple the exchange terms in both the low-order and higher-order Green's functions. As a first numerical example we apply the theory to a monolayer for spin S=1 in order to demonstrate the superiority of the present treatment of the anisotropy terms over the previous approximate decouplings.

23 pages, 5 figures

Cited by in corpus (12)

• Theory of field induced spin reorientation transition in thin Heisenberg films
• Quantum Monte Carlo simulation of thin magnetic films
• Anisotropy effects on the magnetic excitations of a ferromagnetic monolayer below and above the Curie temperature
• Thermodynamics of Heisenberg ferromagnets with arbitrary spin in a magnetic field
• Thermodynamics of S>=1 ferromagnetic Heisenberg chains with uniaxial single-ion anisotropy
• Many-body Green's function theory of ferromagnetic Heisenberg systems with single-ion anisotropies in more than one direction
• The spectral theorem of many-body Green's function theory when there are zero eigenvalues of the matrix governing the equations of motion
• Single-ion versus exchange anisotropy in calculating anisotropic susceptibilities of thin ferromagnetic Heisenberg films within many-body Green's function theory
• The treatment of zero eigenvalues of the matrix governing the equations of motion in many-body Green's function theory
• Anisotropic susceptibilities of thin ferromagnetic films within many-body Green's function theory
• Coupled ferro-antiferromagnetic Heisenberg bilayers investigated by many-body Green's function theory
• The magnetic reorientation transition in thin ferromagnetic films treated by many-body Green's function theory